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1.
We report in this work a transmission electron microscopy study of phase morphologies of environmentally responsive mixed poly( t-butyl acrylate) (P tBA)/polystyrene (PS) brushes and mixed poly(acrylic acid) (PAA)/PS brushes on 180 nm silica particles after treatments with nonselective good solvents and selective solvents, respectively. Mixed P tBA/PS brushes were grown from Y-initiator-functionalized silica particles by sequential atom transfer radical polymerization and nitroxide-mediated radical polymerization. Mixed PAA/PS brushes were prepared from mixed P tBA/PS brushes by removal of the t-butyl groups. For mixed P tBA/PS brushes with P tBA M n of 24.2 kDa and PS M n of 23.0 kDa and the corresponding mixed PAA/PS brushes, random worm-like, nearly bicontinuous nanostructures were formed from lateral microphase separation when the particles were cast from nonselective good solvents (chloroform for mixed P tBA/PS brushes and N, N-dimethylformamide for mixed PAA/PS brushes). The feature sizes were on the order of polymer chain root-mean-square end-to-end distances ( approximately 10 nm). In contrast, mixed P tBA/PS brushes with lower molecular weights (P tBA M n = 10.4 kDa and PS M n = 11.9 kDa) did not strongly phase separate after being cast from chloroform. After the solvents in the particle dispersions were gradually changed to selective solvents ( n-octane for mixed P tBA/PS brushes and H 2O for mixed PAA/PS brushes), isolated microdomains with an average size of 14-19 nm were formed as one grafted polymer collapsed and associated to form isolated microdomains, which were shielded by another grafted polymer yielding surface-tethered micellar structures. These results confirmed the theoretical predictions of the formation of "rippled" nanostructures and surface micellar structures of mixed homopolymer brushes induced by nonselective and selective solvents, respectively.  相似文献   

2.
In this study, we describe a new strategy for producing narrowly dispersed functional colloidal particles stabilized by a nanocomposite with hydrophilic clay faces and hydrophobic polystyrene (PS) brushes on the edges. This method involves preparation of polymer brushes on the edges of clay layers and Pickering suspension polymerization of styrene in the presence of the nanocomposites. PS brushes on the edges of clay layers were prepared by atom transfer radical polymerization. X‐ray diffraction and thermogravimetric analysis results indicated that PS chains were grafted to the edges of clay platelets. Transmission electron microscope results showed that different morphologies of clay‐PS particles could be obtained in different solvents. In water, clay‐PS particles aggregated together, in which PS chains collapsed forming nanosized hydrophobic domains and hydrophilic clay faces stayed in aqueous phase. In toluene, clay‐PS particles formed face‐to‐face structure. Narrowly dispersed PS colloidal particles stabilized by clay‐PS were prepared by suspension polymerization. Because of the negatively charged clay particles on the surface, the zeta potential of the PS colloidal particles was negative. Positively charged poly(2‐vinyl pyridine) (P2VP) chains were adsorbed to the surface of PS colloidal particles in aqueous solution at a low pH value, and gold nanoparticles were prepared in P2VP brushes. Such colloidal particles may find important applications in a variety of fields including waterborne adhesives, paints, catalysis of chemical reactions, and protein separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1535–1543, 2009  相似文献   

3.
We introduce a new lithographic method for the generation of 2D patterns of composite nanoparticles (NPs) of Ag and Au by taking recourse to combine top-down and bottom-up approaches. Micrometer-scale and submicrometer-scale patterned Ag foils of commercially available compact disks (CDs) and digital versatile disks (DVDs), respectively, were used as templates. The galvanic replacement reaction of Ag by HAuCl(4) in the presence of the dye coatings on the foils led to the formation of patterned NP composites of Ag and Au, in addition to the formation of AgCl. The resultant structures appeared in the form of cross patterns of particles with micrometer and submicrometer dimensions. The AgCl crystals thus formed could be removed by using either a saturated NaCl solution or aqueous ammonia. In addition, AgCl could be converted to Ag by electrochemical reduction, thus generating Ag-coated Au NPs. Interestingly, the digital writing on CDs led to the formation of tertiary imprints on the patterns, based on the original writing patterns. This provided an additional handle in generating hierarchical patterns using light in combination with a chemical reaction diffusion process and the nearly parallel line patterns originally present in commercial CDs. The reactions could be carried out in aqueous solution, and the method does not require any additional curing. Also, the density of patterned particles is scalable on the basis of the choice of the original line patterns as present in CDs and DVDs.  相似文献   

4.
A polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) micellar structure with a P2VP core containing 5 nm CdS nanoparticles (NPs) and a PS shell formed in toluene that is a good solvent for PS block undergoes the core‐shell inversion by excess addition of methanol that is a good solvent for P2VP block. It leads to the formation of micellar shell‐embedded CdS NPs in the methanol major phase. The spontaneous crystalline growth of Au NPs on the CdS surfaces positioned at micellar shells without a further reduction process is newly demonstrated. The nanostructure of Au/CdS/PS‐b‐P2VP hybrid NPs is confirmed by transmission electron microscopy, energy‐dispersive X‐ray, and UV‐Vis absorption.

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5.
We use Dip-Pen Nanolithography (DPN) to generate monolayer surface templates for guiding pattern formation in spin-coated polymer blend films. We study template-directed pattern formation in blends of polystyrene/poly(2-vinylpyridine) (PS/P2VP) as well as blends of PS and the semiconducting conjugated polymer poly(3-hexylthiophene) (P3HT). We show that acid-terminated monolayers can be used to template pattern formation in PS/P3HT blends, while hydrophobic monolayers can be used to template pattern formation in PS/P2VP blends. In both blends, the polymer patterns comprise laterally-phase separated regions surrounded by vertically separated bilayers. We hypothesize that the observed patterns are formed by template-induced dewetting of the bottom layer of a polymer bilayer during the spin-coating process. We compare the effects of template feature size and spacing on the resulting polymer patterns with predictions from published models of template-directed dewetting in thin films and find the data in good agreement. For both blends we observe that a minimum feature size is required to nucleate dewetting/phase separation. We find this minimum template diameter to be approximately 180 nm in 50/50 PS/P2VP blends, and approximately 100 nm in 50/50 PS/P3HT blends. For larger template diameters, PS/P2VP blends show evidence for pattern formation beginning at the template boundaries, while PS/P3HT blends rupture randomly across the template features.  相似文献   

6.
Surface-tethered oppositely charged weak polyelectrolyte block copolymer brushes composed of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) were grown from the Si wafer by atom-transfer radical polymerization. The P2VP-b-PAA brushes were prepared through hydrolysis of the second PtBA block to the corresponding acrylic acid. The P2VP-b-PAA brushes with different PAA block length were obtained. The P2VP-b-PAA brushes revealed a unique reversible wetting behavior with pH. The difference between the solubility parameters for P2VP and PAA, the changes of surface chemical composition and surface roughness, and the reversible wetting behavior illustrated that the surface rearrangement occurred during treatment of the P2VP-b-PAA brushes by aqueous solution with different pH value. The reversible properties of the P2VP-b-PAA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.  相似文献   

7.
Gold nanoparticles (Au NPs) were prepared by the reduction of HAuCl4 acid incorporated into the polar core of poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) copolymer micelles dissolved in toluene. The formation of Au NPs was controlled using three reducing agents with different strengths: hydrazine (HA), triethylsilane (TES), and potassium triethylborohydride (PTB). The formation of Au NPs was followed by transmission electron microscopy, UV–Vis spectroscopy, isothermal titration calorimetry (ITC), and dynamic light scattering (DLS). It was found that the strength of the reducing agent determined both the size and the rate of formation of the Au NPs. The average diameters of the Au NPs prepared by reduction with HA, TES, and PTB were 1.7, 2.6, and 8 nm, respectively. The reduction of Au(III) was rapid with HA and PTB. TES proved to be a mild reducing agent for the synthesis of Au NPs. DLS measurements demonstrated swelling of the PS-b-P2VP micelles due to the incorporation of HAuCl4 and the reducing agents. The original micellar structure rearranged during the reduction with PTB. ITC measurements revealed that some chemical reactions besides Au NPs formation also occurred in the course of the reduction process. The enthalpy of formation of Au NPs in PS-b-P2VP micelles reduced by HA was determined.  相似文献   

8.
Encapsulating Au nanoparticles within a shell of photo-cross-linked block copolymer surfactant dramatically improves the physical and chemical stability of the nanoparticles, particularly when they are applied as bioconjugates. Photo-cross-linkable block copolymer amphiphiles [polystyrene-co-poly(4-vinyl benzophenone)]-block-poly(acrylic acid) [(PS-co-PVBP)-b-PAA] and [poly(styrene)-co-poly(4-vinyl benzophenone)]-block-poly(ethylene oxide) [(PS-co-PVBP)-b-PEO] were assembled around Au nanoparticles ranging from 12 to 108 nm in diameter. UV irradiation cross-linked the PVBP groups on the polymer to yield particles that withstood extremes of temperature, ionic strength, and chemical etching. Streptavidin was attached to [PS-co-PVBP]-b-PAA-coated particles using the same noncovalent and covalent conjugation protocols used to bind biomolecules to divinylbenzene-cross-linked PS microspheres. We expect that these particles will be useful as plasmonic, highly light-scattering and light-absorbing analogs to fluorescently labeled PS nanospheres.  相似文献   

9.
Thermally stable core–shell gold nanoparticles (Au NPs) with highly grafted polymer shells were synthesized by combining reversible addition‐fragmentation transfer (RAFT) polymerization and click chemistry of copper‐catalyzed azide‐alkyne cycloaddition (CuAAC). First, alkyne‐terminated poly(4‐benzylchloride‐b‐styrene) (alkyne‐PSCl‐b‐PS) was prepared from the alkyne‐terminated RAFT agent. Then, an alkyne‐PSCl‐b‐PS chain was coupled to azide‐functionalized Au NPs via the CuAAC reaction. Careful characterization using FT‐IR, UV–Vis, and TGA showed that PSCl‐b‐PS chains were successfully grafted onto the Au NP surface with high grafting density. Finally, azide groups were introduced to PSCl‐b‐PS chains on the Au NP surface to produce thermally stable Au NPs with crosslinkable polymer shell ( Au‐PSN3b‐PS 1 ). As the control sample, PS‐b‐PSN3‐coated Au NPs ( Au‐PSN3b‐PS 2 ) were made by the conventional “grafting to” approach. The grafting density of polymer chains on Au‐PSN3b‐PS 1 was found to be much higher than that on Au‐PSN3b‐PS 2 . To demonstrate the importance of having the highly packed polymer shell on the nanoparticles, Au‐PSN3b‐PS 1 particles were added into the PS and PS‐b‐poly(2‐vinylpyridine) matrix, respectively. Consequently, it was found that Au‐PSN3b‐PS 1 nanoparticles were well dispersed in the PS matrix and PS‐b‐P2VP matrix without any aggregation even after annealing at 220 °C for 2 days. Our simple and powerful approach could be easily extended to design other core–shell inorganic nanoparticles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011  相似文献   

10.
An ordered nanostructure can be created from the hybrid materials of self-assembly poly(3-hexyl thiophene-b-2-vinyl pyridine) and nicotinic acid-modified titanium dioxide nanoparticles (P3HT-b-P2VP/TiO(2)). TEM and XRD analyses reveal that the TiO(2) nanoparticles (NPs) are preferentially confined in the P2VP domain of P3HT-b-P2VP whereas TiO(2) NPs interact with either pure P3HT or a blend of P3HT and P2VP to produce microsized phase segregation. The morphologies of lamellar and cylindrical structures are disturbed when the loading of TiO(2) NPs is 40 wt % or higher. Cylindrical P3HT-b-P2VP/TiO(2) exhibits a small blue shift in absorption and photoluminescence spectra with increasing TiO(2) loading as compared to P3HT/TiO(2). The NPs cause a slightly misaligned P3HT domain in the copolymer. Furthermore, the PL quenching of P3HT-b-P2VP/TiO(2) becomes very large as a result of efficient charge separation in the ordered nanodomain at 16 nm. Solar cells fabricated from self-assembly P3HT-b-P2VP/TiO(2) hybrid materials exhibit a >30 fold improvement in power conversion efficiency as compared to the corresponding 0.3P3HT-0.7P2VP/TiO(2) polymer blend hybrid. This study paves the way for the further development of high-efficiency polymer-inorganic nanoparticle hybrid solar cells using a self-assembled block copolymer.  相似文献   

11.
Monodisperse stimuli-responsive hydrogel capsules were synthesized in the 100-nm-diameter to 10-μm-diameter range from poly(4-vinylpyridine) (P4VP) and poly(ethyleneimine) (PEI) through a simple, efficient two-step cross-linking-precipitation template method under conditions of a good solvent. In this method, the core-shell particles were obtained by the deposition (heterocoagulation mechanism) of the cross-linked P4VP, PEI, or their mixtures on the surfaces of the template colloidal silica particles in nitromethane (for PEI) or a nitromethane-acetone mixture (for P4VP and P4VP-PEI mixtures) in the presence of cross-linker 1,4-diiodobutane. The cross-linked polymeric shell swollen in a good solvent stabilized the core-shell colloids. This mechanism provided the conditions for the synthesis of core-shell colloids in a submicrometer range of dimensions with an easily adjusted shell thickness (wall of the capsules) ranging from a few to hundreds of nanometers. The chemical composition of the shell was tuned by varying the ratio of co-cross-linked shell-forming polymers (P4VP and PEI). In the second step, the hollow capsules were obtained by etching the silica core in HF solutions. In this step, the colloidal stability of the hollow capsules was provided by ionized P4VP and PEI cross-linked shells. The hollow capsules demonstrate that the pH- and ionic-strength-triggered swelling and shrinking result in size-selective uptake and release properties. Cross-linked via quaternized functional groups, P4VP capsules undergo swelling and shrinking transitions at a physiologically relevant pH of around 6. The 200-nm-diameter hollow capsule with 25-nm-thick walls demonstrated a factor of 2 greater capacity to accommodate cargo molecules than the core-shell particles of the same dimensions because of an internal compartment and a combination of radial and a circumferential swelling modes in the capsules.  相似文献   

12.
杨木泉  肖凌宇  张旋  颜悦 《应用化学》2019,36(4):431-439
作为受限高分子体系的一个经典模型,高分子刷在胶体稳定、聚合物链的自组装以及摩擦学等方面具有潜在的应用价值。 本文通过原子转移自由基聚合(ATRP)和点击化学(Click Chemistry)方法在金(Au)基底表面制备了pH响应性聚4-乙烯基吡啶-b-聚乙二醇(P4VP-b-PEG)嵌段聚合物刷。 通过频率-耗散型石英微天平(QCM-D)、X射线光电子能谱(XPS)和原子力显微镜(AFM)等技术手段分别对Au/P4VP-b-PEG聚合物刷经不同pH值溶液处理后的形态变化、表面组成和表面形貌进行了进一步深入研究。 结果表明,用不同pH值溶液处理P4VP-b-PEG嵌段聚合物刷后,该聚合物刷呈现刺激响应规律。 当pH=1.5时,P4VP链段质子化,由于静电排斥作用使P4VP-b-PEG链段呈伸展构象;当pH=11.5时,P4VP链段去质子化,并且由于失去部分结合水,P4VP-b-PEG链段呈塌缩构象。  相似文献   

13.
We report a facile strategy to synthesize amphiphilic gold (Au) nanoparticles functionalized with a multilayer, micelle-like structure consisting of a Au core, an inner hydroxylated polyisoprene (PIOH) layer, and an outer polystyrene shell (PS). Careful control of enthalpic interactions via a systematic variation of structural parameters, such as number of hydroxyl groups per ligand (N(OH)) and styrene repeating units (N(PS)) as well as areal chain density of ligands on the Au-core surface (Σ), enables precise control of the spatial distribution of these nanoparticles. This control was demonstrated in a lamellae-forming poly(styrene-b-2-vinylpyridine) (PS-b-P2VP) diblock copolymer matrix, where the favorable hydrogen-bonding interaction between hydroxyl groups in the PIOH inner shell and P2VP chains in the PS-b-P2VP diblock copolymer matrix, driving the nanoparticles to be segregated in P2VP domains, could be counter balanced by the enthalphic penalty of mixing of the PS outer brush with the P2VP domains. By varying N(OH), N(PS), and Σ, the nanoparticles could be positioned in the PS or P2VP domains or at the PS/P2VP interface. In addition, the effect of additives interfering with the hydrogen-bond formation between hydroxyl groups on Au nanoparticles and P2VP chains in a diblock copolymer matrix was investigated, and an interesting pea-pod-like segregation of Au nanoparticles in PS domains was observed.  相似文献   

14.
We investigated the adhesive properties of binary heterogeneous polymer brushes made from end-functionalized polystyrene (PS) and poly(2-vinylpyridine) (P2VP) chains. The molecular organization of the mixed brush could be varied reversibly by exposure to selective solvents for PS (toluene) and for P2VP (acidic water). This exposure results in reversible switching of adhesive and wetting properties. The manner in which the adhesion switching occurs can be tuned by the composition of mixed brushes. However, the outer surface composition could be enriched more effectively in PS after the toluene treatment than in P2VP after the acidic water treatment. As a result, the mixed brush compositions that showed the largest difference in properties between an exposure to toluene and an exposure to water were the P2VP-rich compositions. Adhesive properties, tested against a soft hydrophobic pressure-sensitive adhesive (PSA) using a probe test, always showed smaller differences between solvent treatments than wetting properties with water, suggesting a much higher sensitivity of the hydrophobic/hydrophilic brushes to polar molecules than to nonpolar molecules.  相似文献   

15.
A new procedure is described for surface grafting polymer brushes by step-growth polymerization from initiator-embedded polymeric thin films and micron- and nanometer-scale patterns. An imprint lithographic process, nanocontact molding, was used to prepare thin patterned cross-linked polyacrylate network films on silicon wafers that incorporated 4-bromostyrene in the networks. These networks present reactive 4-bromophenyl functionality at the surface that act as attachment sites for the subsequent Ni(0)- mediated step-growth condensation polymerization of 2,7-dibromo-9,9-dihexylfluorene The step-growth polymerization medium consisted of 2,7-dibromo-9,9-dihexylfluorene, Ni(0)-catalyst, and bipyridine in a toluene/dimethylformamide solvent mixture. The resulting growth of polydihexylfluorene brushes from the patterned surface was monitored by contact angle, optical spectrometry, surface profilometry and AFM. Brush growth was conducted from patterned features ranging from 100 microm to 100 nm in width and 50 nm in height. The optical and fluorescence behavior of the polyfluorene brushes was similar to that of thin polyfluorene films made by spin coating.  相似文献   

16.
Herein we report the generation of Au nanoparticles (NPs) by sparingly soluble acetanilide in water. We also report the formation of linear chain-like superstructures of self-assembled Au NPs, in the presence of excess acetanilide. This was achieved in two different ways. In the first method, acetanilide was added, with increasing concentration, into aqueous HAuCl(4) to produce Au NPs as well as for the formation of assembly, which varied according to the concentration of acetanilide. The other route involved formation of spherical Au NPs at the lowest concentration of acetanilide, which was followed by the formation of assembly of various lengths upon further addition of variable amount of acetanilide. The assemblies were stable in aqueous solution for days with characteristic UV-vis absorption spectra consisting of two peaks. While the wavelength of the first peak remained the same, the position of the second peak changed to longer wavelength with increasing acetanilide concentration. Interestingly, the linear chain-like arrays could be broken into individual particles by first dilution of the solution concentration followed by treatment with ultrasonic waves. The individual Au NPs again formed linear chain-like arrays upon addition of excess acetanilide.  相似文献   

17.
Pseudomonas aeruginosa were used for extra-cellular biosynthesis of gold nanoparticles (Au NPs). Consequently, Au NPs were formed due to reduction of gold ion by bacterial cell supernatant of P. aeruginosa ATCC 90271, P. aeruginosa (2) and P. aeruginosa (1). The UV-vis and fluorescence spectra of the bacterial as well as chemical prepared Au NPs were recorded. Transmission electron microscopy (TEM) micrograph showed the formation of well-dispersed gold nanoparticles in the range of 15-30 nm. The process of reduction being extra-cellular and may lead to the development of an easy bioprocess for synthesis of Au NPs.  相似文献   

18.
Plasmonic superstructures (PS) based on Au/SiO2 were prepared for Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy (SHINERS) in liquid phase applications. These superstructures are composed of functionalized SiO2 spheres with plasmonic Au nanoparticles (NPs) on their surface. Functionalization was performed with (3-aminopropyl)trimethoxysilane, (3-mercaptopropyl)trimethoxysilane and poly(ethylene-imine) (PEI). Of these three, PEI-functionalized spheres showed the highest adsorption density of Au NPs in TEM, UV/Vis and dynamic light scattering (DLS) experiments. Upon decreasing the Au NP/SiO2 sphere size ratio, an increase in adsorption density was also observed. To optimize plasmonic activity, 61 nm Au NPs were adsorbed onto 900 nm SiO2-PEI spheres and these PS were coated with an ultrathin layer (1–2 nm) of SiO2 to obtain Shell-Isolated Plasmonic Superstructures (SHIPS), preventing direct contact between Au NPs and the liquid medium. Zeta potential measurements, TEM and SHINERS showed that SiO2 coating was successful. The detection limit for SHINERS using SHIPS and a 638 nm laser was around 10−12 m of Rhodamine (10−15 m for uncoated PS), all with acquisition settings suitable for catalysis applications.  相似文献   

19.
We report on the growth of gold nanoparticles in polystyrene/poly(2-vinyl pyridine) (PS/P2VP) star-shaped block copolymer monolayers. These amphiphilic PS(n)P2VP(n) heteroarm star copolymers differ in molecular weight (149,000 and 529,000 Da) and the number of arms (9 and 28). Langmuir-Blodgett (LB) deposition was utilized to control the spatial arrangement of P2VP arms and their ability to reduce gold nanoparticles. The PS(n)P2VP(n) monolayer acted as a template for gold nanoparticle growth because of the monolayer's high micellar stability at the liquid-solid interface, uniform domain morphology, and ability to adsorb Au ions from the water subphase. UV-vis spectra and AFM and TEM images confirmed the formation of individual gold nanoparticles with an average size of 6 ± 1 nm in the P2VP-rich outer phase. This facile strategy is critical to the formation of ultrathin polymer-gold nanocomposite layers over large surface areas with confined, one-sided positioning of gold nanoparticles in an outer P2VP phase at polymer-silicon interfaces.  相似文献   

20.
Water-in-oil (W/O) emulsion-induced micelles with narrow size distributions of approximately 140 nm were prepared by sonicating the polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer in the toluene/water (50:1 vol %). The ordered nanoporous block copolymer films with the hydrophilic P2VP interior and the PS matrix were distinctly fabricated by casting the resultant solution on substrates, followed by evaporating the organic solvent and water. The porous diameter was estimated to be about 70 nm. Here, we successfully prepared the open nanoporous nanocomposites, the P2VP domain decorated by Au (5+/-0.4 nm) nanoparticles based on the methodology mentioned. We anticipate that this novelty enhances the specific function of nanoporous films.  相似文献   

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